fmax.hpp

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#ifndef STAN__AGRAD__REV__FUNCTIONS__FMAX_HPP
#define STAN__AGRAD__REV__FUNCTIONS__FMAX_HPP

#include <stan/agrad/rev/var.hpp>
#include <boost/math/special_functions/fpclassify.hpp>
#include <stan/agrad/rev/internal/precomp_v_vari.hpp>
#include <stan/agrad/rev/internal/precomputed_gradients.hpp>
#include <stan/math/constants.hpp>
#include <stan/meta/likely.hpp>

namespace stan {
  namespace agrad {

    inline var fmax(const stan::agrad::var& a,
                    const stan::agrad::var& b) {
      if (unlikely(boost::math::isnan(a.vi_->val_))) {
        if(boost::math::isnan(b.vi_->val_)) {
          std::vector<stan::agrad::var> vars;
          std::vector<double> grads;
          vars.push_back(a);
          vars.push_back(b);
          grads.push_back(stan::math::NOT_A_NUMBER);
          grads.push_back(stan::math::NOT_A_NUMBER);
          return var(precomputed_gradients(stan::math::NOT_A_NUMBER,
                                           vars, grads));
        }
        else
          return b;
      } else if (unlikely(boost::math::isnan(b.vi_->val_)))
        return a;
      else
        return a.vi_->val_ > b.vi_->val_ ? a : b;
    }

    inline var fmax(const stan::agrad::var& a,
                    const double& b) {
      if (unlikely(boost::math::isnan(a.vi_->val_))) {
        if(boost::math::isnan(b))
          return var(new precomp_v_vari(stan::math::NOT_A_NUMBER,
                                        a.vi_,
                                        stan::math::NOT_A_NUMBER));
        else
          return var(b);
      } else if (unlikely(boost::math::isnan(b)))
        return a;
      else
        return a.vi_->val_ >= b ? a : var(b);
    }

    inline var fmax(const double& a,
                    const stan::agrad::var& b) {
      if (unlikely(boost::math::isnan(b.vi_->val_))) {
        if(boost::math::isnan(a))
          return var(new precomp_v_vari(stan::math::NOT_A_NUMBER,
                                        b.vi_,
                                        stan::math::NOT_A_NUMBER));
        else
          return var(a);
      } else if (unlikely(boost::math::isnan(a)))
        return b;
      else
        return a > b.vi_->val_ ? var(a) : b;
    }

  }
}
#endif